Measured Pressure Waveforms Research Articles

Efficacy and safety of pulmonary artery catheterization with combined transesophageal echocardiography and pressure waveform: A prospective observational study

ObjectiveThis study investigated whether pulmonary artery catheter placement method with combined transesophageal echocardiography and pressure waveform measurement improve the placement success rate within 5 min and reduce the incidence of arrhythmia during pulmonary artery catheter placement compared to conventional pulmonary artery catheter placement with pressure waveform measurement only. MethodsThis single center prospective observational study included 129 patients scheduled for cardiac surgery. Patients were divided into two groups. In the conventional group, the pulmonary artery catheter was placed by monitoring the pressure waveform and the length of placement; in the combination group, not only were the pressure waveform and the length monitored but also the following transesophageal echocardiography images: “mid esophageal bicaval view,” " mid esophageal modified bicaval view,” a mirror image of “mid esophageal 4 chamber view,” “mid esophageal right ventricular inflow-outflow view,” and “mid esophageal ascending aortic short axis view." ResultsA 1:1 propensity score matching was used to adjust for confounding factors. The success rates of pulmonary artery catheter placement within 5 min in the conventional and combination groups were 85.5 % vs. 97.8 % (p = 0.032) before matching, and 73.7 % vs. 100 % (p = 0.001) after matching. The incidences of arrhythmias in the conventional and combination groups were 28.9 % vs. 17.4 % (p = 0.20) before matching, and 28.9 % vs. 18.4 % (p = 0.42) after matching. ConclusionPulmonary artery catheter placement with transesophageal echocardiography had a significantly higher rate of successful placement within 5 min, but no significant differences were observed in the incidences of arrhythmias.

NON-INVASIVE CENTRAL BLOOD PRESSURE AND INTRACRANIAL WAVEFORM ASSESSMENT IN HYPERTENSIVE PATIENTS

Objective: Hypertension (HT) remains as the leading cause of death around the globe and brain diseases, such as cognitive decline. The association between HT and cerebrovascular diseases is strong, mainly with stroke and cognitive impairment, but the mechanistic bases remain to be established. The objective of this study is to observe central blood pressure, arterial stiffness and intracranial pressure in long-term chronic hypertensive patients. Design and method: Patients above 18 years were assessed from November 2022 to August 2023 with non-invasive central blood pressure and intracranial pressure waveform measurements in a cross-sectional analysis. Peripheral and central blood pressure parameters were obtained using a validated oscillometric device (Mobil-O-Graph). Non-invasive intracranial pressure measurement was performed with the validated Brain4Care (B4C) sensor. Using the B4C non-invasive evaluation, the cut-off point identified to define ICHT by the P2/P1 ratio was > 1.2, and the cut-off for time to peak (TTP) was > 0.25 seconds. To compare P2/P1 and TTP values between the categories of quantitative variables, the chi-square test was used; the Mann Whitney or ANOVA tests were used for bivariate analyses; and for correlations, the Spearman test was used. It was adopted as significant at p < 0,05. Results: Non-invasive central blood pressure, arterial stiffness, and intracranial pressure waveform assessment were performed in 145 patients with essential long-term hypertension over a period of ten months. The median age was 69.0 (61.8 – 75.7) years, 77.9% were female, and the median BMI was 29.0 (25.4 – 33.1) kg/m2. The average time since the hypertension diagnosis was 20.0 years. The median value of P2/P1 ratio for all cohort was 1.4 (1.2 – 1.5) and TTP 0.24 (0.21 – 0.29) seconds. A bivariate analysis was performed considering ICHT or not and the parameters of central BP and PWV assessments, with findings of higher central SBP, central DBP, and peripheral DBP among patients with ICHT by the parameter of P2/P1. Conclusions: Central systolic blood pressure levels are more linked to intracranial hypertension, while diastolic blood pressure values are similar, raising questions about the most suitable blood pressure assessment method for brain disorders.

Non-invasive assessment of stroke volume and cardiovascular parameters based on peripheral pressure waveform.

Cardiovascular diseases are the leading cause of death globally, making the development of non-invasive and simple-to-use tools that bring insights into the state of the cardiovascular system of utmost importance. We investigated the possibility of using peripheral pulse wave recordings to estimate stroke volume (SV) and subject-specific parameters describing the selected properties of the cardiovascular system. Peripheral pressure waveforms were recorded in the radial artery using applanation tonometry (SphygmoCor) in 35 hemodialysis (HD) patients and 14 healthy subjects. The pressure waveforms were then used to estimate subject-specific parameters of a mathematical model of pulse wave propagation coupled with the elastance-based model of the left ventricle. Bioimpedance cardiography measurements (PhysioFlow) were performed to validate the model-estimated SV. Mean absolute percentage error between the simulated and measured pressure waveforms was 4.0% and 2.8% for the HD and control group, respectively. We obtained a moderate correlation between the model-estimated and bioimpedance-based SV (r = 0.57, p<0.05, and r = 0.58, p<0.001, for the control group and HD patients, respectively). We also observed a correlation between the estimated end-systolic elastance of the left ventricle and the peripheral systolic pressure in both HD patients (r = 0.84, p<0.001) and the control group (r = 0.70, p<0.01). These preliminary results suggest that, after additional validation and possibly further refinement to increase accuracy, the proposed methodology could support non-invasive assessment of stroke volume and selected heart function parameters and vascular properties. Importantly, the proposed method could be potentially implemented in the existing devices measuring peripheral pressure waveforms.

Waveform characteristics in thoracic paravertebral space: a prospective observational study

Background With increased use of thoracic paravertebral block (TPVB) in thoracic surgery, many faced the challenge of locating the thoracic paravertebral space (TPVS) ultrasonographically. This observational study aimed to investigate the waveform characteristics and pressure value within the TPVS in anaesthetized patients with controlled ventilation. Methods 50 patients scheduled for elective lung surgery were enrolled. After conduction of anesthesia, all patients underwent TPVB at T4/5 and T6/7 using transverse, in-plane ultrasound guidance. A pressure transducer system with a desktop monitor was connected to the needle hub to measure pressure values and waveform characteristics in three locations: the paraspinal muscles, immediately behind the superior costotransverse ligament, and within the TPVS. Next, 15 mL of 0.33% bupivacaine was injected into each desired TPVS. After completion of the surgery, the extent of dermatomal blockade and the pain score was assessed in all patients. Results 98 typical regular respiratory waveforms with a mean pressure of ≤ 25 mmHg were detected in the TPVS of 50 patients. The sensitivity of the combined ultrasound and pressure waveform measurement technique to identify the TPVS was 95.45% (95% confidence interval, 84.527–99.445). Nontypical respiratory waveforms were present in two patients. Factors interfering with the TPVS waveform characteristics were previous thoracic surgery and chronic pleural inflammation. Conclusion The TPVS had low pressure and showed a smooth, regular waveform pattern corresponding to respiration.

Assessment of Aortic Characteristic Impedance and Arterial Compliance from Non-invasive Carotid Pressure Waveform in The Framingham Heart Study

The primary goal of this study was to test the hypothesis that a hybrid intrinsic frequency-machine learning (IF-ML) approach can accurately evaluate total arterial compliance (TAC) and aortic characteristic impedance (Zao) from a single noninvasive carotid pressure waveform in both women and men with heart failure (HF). TAC and Zao are cardiovascular biomarkers with established clinical significance. TAC is lower and Zao is higher in women than in men, so women are more susceptible to the consequent deleterious effects of them. Although the principles of TAC and Zao are pertinent to a multitude of cardiovascular diseases, including HF, their routine clinical use is limited because of the requirement for simultaneous measurements of flow and pressure waveforms. For this study, the data were obtained from the Framingham Heart Study (n=6,201, 53% women). The reference values of Zao and TAC were computed from carotid pressure and aortic flow waveforms. IF parameters of carotid pressure waveform were used in ML models. IF models were developed on n=5,168 of randomly selected data and blindly tested the remaining data (n=1,033). The final models were evaluated in patients with HF. Correlations between IF-ML and reference values in all HF and HF with preserved ejection fraction for TAC were 0.88 and 0.90, and for Zao were 0.82 and 0.80, respectively. The classification accuracy in all HF and HF with preserved ejection fraction for TAC were 0.9 and 0.93, and for Zao were 0.81 and 0.89, respectively. In conclusion, the IF-ML method provides an accurate estimation of TAC and Zao in all subjects with HF and in the general population.

Online continuous measurement of arterial pulse pressure and pressure waveform using ultrasound

Noninvasive measurement of local pulse pressure (PP) and blood pressure waveforms, especially in central arteries, is crucial for diagnosing and preventing cardiovascular diseases (CVDs). This work presents an ultrasound system that uses a low-computational method to evaluate local pulse wave velocity (PWV) and diameter waveforms online, enabling continuous and noninvasive measurement of PP and blood pressure waveforms without calibration. The system was validated both in vitro and in vivo, demonstrating high accuracy in PP and blood pressure waveform measurements in cardiovascular phantom experiments. In human carotid experiments, the system was compared to an arterial tonometer, showing excellent accuracy in PP and pressure waveform similarity. Comparative experiments with the volume clamp device further demonstrated the system's ability to accurately trace blood pressure changes induced by deep breathing. Thus, the developed system holds promise for noninvasively measuring arterial PP and blood pressure waveforms continuously, facilitating the diagnosis and prevention of CVDs.

Non-Invasive Pressure-Only Aortic Wave Intensity Evaluation Using Hybrid Fourier Decomposition-Machine Learning Approach.

The clinical significance of the wave intensity (WI) analysis for the diagnosis and prognosis of the cardiovascular and cerebrovascular diseases is well-established. However, this method has not been fully translated into clinical practice. From practical point of view, the main limitation of WI method is the need for concurrent measurements of both pressure and flow waveforms. To overcome this limitation, we developed a Fourier-based machine learning (F-ML) approach to evaluate WI using only the pressure waveform measurement. Tonometry recordings of the carotid pressure and ultrasound measurements for the aortic flow waveforms from the Framingham Heart Study (2640 individuals; 55% women) were used for developing the F-ML model and the blind testing. Method-derived estimates are significantly correlated for the first and second forward wave peak amplitudes (Wf1, r = 0.88, p 0.05; Wf2, r = 0.84, p 0.05) and the corresponding peak times (Wf1, r = 0.80, p < 0.05; Wf2, r = 0.97, p 0.05). For backward components of WI (Wb1), F-ML estimates correlated strongly for the amplitude (r = 0.71, p 0.05) and moderately for the peak time (r = 0.60, p 0.05). The results show that the pressure-only F-ML model significantly outperforms the analytical pressure-only approach based on the reservoir model. In all cases, the Bland-Altman analysis shows negligible bias in the estimations. The proposed pressure-only F-ML approach provides accurate estimates for WI parameters. The pressure only F-ML approach introduced in this work expand the clinical usage of WI into inexpensive and non-invasive settings such as wearable telemedicine.

Precise Observation of Ultrasonic Pulses Using an SPR Sensor

Surface plasmon resonance (SPR) type ultrasonic sensors enable local measurements and have a flat frequency response in a wide frequency range. They are expected to be used in photoacoustic microscopy (PAM) and other applications that require broadband ultrasonic detection. In this study, we focus on the precise measurement of ultrasound pressure waveforms via a Kretschmann-type SPR sensor. The noise equivalent pressure was estimated to be 52 Pa [Formula: see text], and the maximum amplitude of the wave measured via the SPR sensor linearly responded to the pressure until 427 kPa [Formula: see text]. Furthermore, the observed waveform for each applied pressure agreed well with the waveforms measured via the calibrated ultrasonic transducer (UT) in the MHz range. Moreover, we focused on the effect of the sensing diameter on the frequency response of the SPR sensor. The results show that the beam diameter reduction improved the frequency response at high frequencies. Evidently, we found that the sensing diameter of the SPR sensor must be carefully selected in consideration of the measurement frequency.

Model-Based Fluid-Structure Interaction Approach for Evaluation of Thoracic Endovascular Aortic Repair Endograft Length in Type B Aortic Dissection.

Thoracic endovascular aortic repair (TEVAR) is a commonly performed operation for patients with type B aortic dissection (TBAD). The goal of TEVAR is to cover the proximal entry tear between the true lumen (TL) and the false lumen (FL) with an endograft to induce FL thrombosis, allow for aortic healing, and decrease the risk of aortic aneurysm and rupture. While TEVAR has shown promising outcomes, it can also result in devastating complications including stroke, spinal cord ischemia resulting in paralysis, as well as long-term heart failure, so treatment remains controversial. Similarly, the biomechanical impact of aortic endograft implantation and the hemodynamic impact of endograft design parameters such as length are not well-understood. In this study, a fluid-structure interaction (FSI) computational fluid dynamics (CFD) approach was used based on the immersed boundary and Lattice–Boltzmann method to investigate the association between the endograft length and hemodynamic variables inside the TL and FL. The physiological accuracy of the model was evaluated by comparing simulation results with the true pressure waveform measurements taken during a live TEVAR operation for TBAD. The results demonstrate a non-linear trend towards increased FL flow reversal as the endograft length increases but also increased left ventricular pulsatile workload. These findings suggest a medium-length endograft may be optimal by achieving FL flow reversal and thus FL thrombosis, while minimizing the extra load on the left ventricle. These results also verify that a reduction in heart rate with medical therapy contributes favorably to FL flow reversal.

Accuracy and applicability of non-invasive evaluation of aortic wave intensity using only pressure waveforms in humans

Background. Wave intensity (WI) analysis is a well-established method for quantifying the energy carried in arterial waves, providing valuable clinical information about cardiovascular function. The primary drawback of this method is the need for concurrent measurements of both pressure and flow waveforms. Objective. We have for the first time investigated the accuracy of a novel methodology for estimating wave intensity employing only single pressure waveform measurements; we studied both carotid- and radial-based estimations in a large heterogeneous cohort. Approach. Tonometry was performed alongside Doppler ultrasound to acquire measurements of both carotid and radial pressure waveforms as well as aortic flow waveforms in 2640 healthy and diseased participants (1439 female) in the Framingham Heart Study. Patterns consisting of two forward waves (Wf1, Wf2) and one backward wave (Wb1) along with reflection metrics were compared with those obtained from exact WI analysis. Main Results. Carotid-based estimates correlated well for forward peak amplitudes (Wf1, = 0.85, < 0.05; Wf2, = 0.72, < 0.05) and peak time (Wf1, = 0.94, < 0.05; Wf2, = 0.98, < 0.05), and radial-based estimates correlated fairly to poorly for amplitudes (Wf1, = 0.62, < 0.05; Wf2, = 0.42, < 0.05) and peak time (Wf1, = 0.04, = 0.10; Wf2, = 0.75, < 0.05). In all cases, estimated Wb1 measures were not correlated. Reflection metrics were well correlated for healthy patients ( = 0.67, < 0.05), moderately correlated for valvular disease ( = 0.59, < 0.05) and fairly correlated for CVD ( = 0.46, < 0.05) and heart failure ( = 0.49, < 0.05). Significance. These findings indicate that pressure-only WI produces accurate results only when forward contributions are of primary interest and only for carotid pressure waveforms. The pressure-only WI estimations of this work provide an important opportunity to further the goal of uncovering clinical insights through wave analysis affordably and non-invasively.

An Ingestible Electronics for Continuous and Real-Time Intraabdominal Pressure Monitoring.

Abdominal compartment syndrome can be treated through decompressive surgery if intraabdominal hypertension (IAH) can be detected in time. Treatment delays due to manual, conventional intravesical pressure (IVP) monitoring using a Foley catheter have been reported. In this work, we present an innovative gastrointestinal intraluminal pressure (GIP) measurement-based method to monitor and improve pressure-guided relief of intraabdominal pressure (IAP). A novel algorithm for detecting IAH in the gastrointestinal tract of a live porcine model is reported. A wireless pressure-sensing capsule (10 × 13 mm) was developed for absolute measurement. The IAP was estimated during artificial pneumoperitoneum. The pressure waveform-based measurements indicated that the wireless pressure sensor could be used to predict IAP. To enhance GIP monitoring for predicting IAH, the proposed continuous ingestible wireless electronics-based pressure waveform measurement device can be used as a complement to existing modalities. The use of the proposed pressure measurement and communication technology can help provide valuable data for digital health platforms.

Distortion of the Intracranial Pressure Waveform by Extraventricular Drainage System.

To investigate whether intracranial pressure (ICP) waveform measurements obtained from extraventricular drainage (EVD) systems are suitable for the calculation of intracranial elastance (ICE) or cerebrovascular pressure autoregulation (PAR) indices. The transfer characteristic of an EVD system is investigated by its step and frequency responses with focus on the low frequency (LF) range from 0.02 to 0.065Hz (important in PAR) and the location of the system's first resonance frequency (important for ICE). The effects of opening the distal end of the EVD for drainage of cerebrospinal fluid and the presence of trapped air bubbles are also investigated. The EVD system exhibits a first resonant frequency below 4Hz, resulting in significant distortion of the measured ICP waveform. The frequency response in the LF range only remains flat when the EVD is closed. Opening the drain results in drops in magnitude and phase along the entire frequency range above DC. Air bubbles close to the EVD catheter tip affect the LF range while an air bubble close to the pressure transducer further decreases the first resonant frequency. Tests with actual ICP waveforms confirmed EVD-induced waveform distortions that can lead to erroneous ICE estimation. EVD-based ICP measurements distort the waveform morphology. PAR indices based on LF information are only valid if the EVD is closed. EVD-based ICE estimation is to be avoided. ICP waveform analyses to derive information about ICE and PAR should be critically questioned if only EVD derived ICP signals are at hand.

Feasibility of Estimation of Aortic Wave Intensity Using Non-invasive Pressure Recordings in the Absence of Flow Velocity in Man.

BackgroundWave intensity analysis provides valuable information on ventriculo-arterial function, hemodynamics, and energy transfer in the arterial circulation. Widespread use of wave intensity analysis is limited by the need for concurrent measurement of pressure and flow waveforms. We describe a method that can estimate wave intensity patterns using only non-invasive pressure waveforms (pWIA).MethodsRadial artery pressure and left ventricular outflow tract (LVOT) flow velocity waveforms were recorded in 12 participants in the Southall and Brent Revisited (SABRE) study. Pressure waveforms were analyzed using custom-written software to derive the excess pressure (Pxs) which was scaled to peak LVOT velocity and used to calculate wave intensity. These data were compared with wave intensity calculated using the measured LVOT flow velocity waveform. In a separate study, repeat measures of pWIA were performed on 34 individuals who attended two clinic visits at an interval of ≈1 month to assess reproducibility and reliability of the method.ResultsPxs waveforms were similar in shape to aortic flow velocity waveforms and the time of peak Pxs and peak aortic velocity agreed closely. Wave intensity estimated using pWIA showed acceptable agreement with estimates using LVOT velocity tracings and estimates of wave intensity were similar to values reported previously in the literature. The method showed fair to good reproducibility for most parameters.ConclusionThe Pxs is a surrogate of LVOT flow velocity which, when appropriately scaled, allows estimation of aortic wave intensity with acceptable reproducibility. This may enable wider application of wave intensity analysis to large studies.

Insomnia is Associated with an Increased Carotid‐Femoral Pulse Wave Velocity in Healthy Young Adults during Awake Hours

Current literature indicates that those living with insomnia have an increased risk of developing and dying from cardiovascular disease (CVD). Previous studies have investigated cardiovascular measures such as baroreflex sensitivity (cvBRS), heart rate (HR), blood pressure (BP) and serum lipid levels in those with insomnia, however these studies focus on older adults and do not investigate early cardiovascular changes occurring in a young population. The purpose of this study was to examine differences across multiple cardiovascular measures that may be associated with insomnia in a young, healthy adult population. This cross‐sectional analysis of the midpoint sample of the Niagara Longitudinal Heart Study used data from 156 participants aged 19–25 years. Insomnia was classified using the SLEEP‐50 questionnaire and was compared across measures of BP, HR, cvBRS, and carotid‐femoral pulse wave velocity (cfPWV). HR and BP were measured using an automatic oscillometric device, cvBRS was measured using a beat‐by‐beat systolic BP and RR intervals, and cfPWV was measured using a hand‐held tonometer which measured pressure waveforms. Significantly higher cfPWV was found in those with insomnia (M=6.00± 0.89) versus those without (M=5.57 ±0.88) (p=0.013). There were no significant differences between those with and without insomnia for BP, HR or cvBRS (p&gt;0.05), however, a non‐significant trend in HR was found between those with insomnia (M=79.93± 11.92) and those without (M=75.91± 11.18) (p=0.058). Literature suggests that insomnia may lead to CVD through mechanisms including changes in autonomic activity, systemic inflammation, and hormonal dysregulation. Previous insomnia studies have not investigated cfPWV, therefore these findings suggest that arterial stiffness may be an early indicator of CVD risk in those with insomnia. These results are especially novel since they are being detected in a young, otherwise healthy population suggesting that CVD risk may begin to develop early in those suffering with insomnia. The identification of these differences at a young age suggests that significant cardiovascular change occurs earlier than previously expected in those living with insomnia, thus prompting early intervention to help reduce the physiological burden of this sleeping disorder.Support or Funding InformationFunding source: The NLHS is funded by the Canadian Institutes of Health Research (CIHR #s 363774, 399332). KSD is funded by a CIHR Doctoral Research Award – Frederick Banting and Charles Best Canada Graduate Scholarship (RFN#167014)

Finite-time joint estimation of the arterial blood flow and the arterial Windkessel parameters using modulating functions

Studying the arterial hemodynamic response plays a crucial role in the understanding and the treatment of cardiovascular diseases. Due to the difficulty of measuring the arterial blood flow, its estimation through a particular arterial vessel, using non-invasive arterial pressure waveform measurements, has always been an important topic in physiology. For instance, knowing the blood flow in a specific site of the arterial network helps in the detection of arterial stenosis. It may also help in the diagnosis of heart valve’s diseases. In this paper, an algorithm based on modulating functions is proposed to estimate the arterial blood flow as well as to calibrate the conventional Windkessel model using arterial blood pressure signals measured in a particular site of the arterial system. The algorithm is presented and illustrated through several numerical tests.

Effect of surface roughness on nonlinear reflection of weak shock waves.

The authors have recently shown that irregular reflections of spark-generated pressure weak shocks from a smooth rigid surface can be studied using an optical interferometer [Karzova, Lechat, Ollivier, Dragna, Yuldashev, Khokhlova, and Blanc-Benon, J. Acoust. Soc. Am. 145(1), 26-35 (2019)]. The current study extends these results to the reflection from rough surfaces. A Mach-Zehnder interferometer is used to measure pressure waveforms. Simulations are based on the solution of axisymmetric Euler equations. It is shown that roughness causes a decrease of the Mach stem height and the appearance of oscillations in the pressure waveforms. Close to rough surfaces, the pressure was higher compared to the smooth surface.

Cerebrovascular Compliance is Affected by Posture

The mechanical properties of the arterial vascular wall influence the oscillatory component of flow through a vascular bed. Windkessel modeling has often been used to non‐invasively estimate these mechanical properties. While the systemic and coronary circulation have received considerable attention, the cerebral circulation represents a unique challenge because the oscillatory component of cerebral blood flow occurs within a pressurized and rigid skull. The present investigation evaluated the compliance of the cerebral vascular bed in comparison to that of the forearm vascular bed, a bed without significant extravascular pressure. Six young and healthy adults (24 ± 3 years, 5 females) were instrumented with a 3‐lead electrocardiogram, a finger photoplethysmograph (Finapres Medical Systems), and transcranial Doppler ultrasound (Multigon Industries) for continuous measures of heart rate, arterial blood pressure from the brachial artery, and cerebral blood flow velocity from the middle cerebral artery, respectively. Brachial artery blood flow velocity was also measured (duplex Doppler ultrasound; GE Healthcare). Following stabilization of hemodynamic variables, one to two minutes of data were collected in the supine posture. Measures were repeated after participants transitioned to a sitting posture, following re‐stabilization of variables. A modified Windkessel model was used to calculate the values of vascular compliance, as well as viscoelasticity and inertance effects, that are required to match the measured flow waveform to that predicted from the measured pressure waveform. Estimates of compliance were calculated for the forearm and cerebral vascular beds. In the supine posture, compliance of the cerebral vascular bed was lower than that of the forearm vascular bed by more than one order of magnitude (0.0006 ± 0.0005 vs. 0.002 ± 0.0007 mL/mmHg; P≤0.001; d=2.6). However, when seated, cerebrovascular compliance and forearm vascular compliance were not significantly different (0.002 ± 0.001 vs. 0.003 ± 0.002 mL/mmHg; P=0.10; d=1.0). The compliance in the brain increased considerably from the supine to sitting posture (P=0.03; d=0.91) but no significant difference was observed in the forearm (P=0.13; d=−0.65). The results suggest that intracranial pressure may prevent the cerebral vessels from exercising their compliance in supine. Further, as cerebrovascular compliance is increased with sitting, we speculate that posture‐induced reductions in cerebral venous volume affect cerebrovascular mechanics.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of arterial pressure measurement location on pulse contour stroke volume estimation, during a rapid change in hemodynamic state

Abstract Continuous cardiac output monitors are becoming more common in clinical settings to assess cardiac performance. Pulse contour analysis is a common method employed by commercial devices to estimate patient hemodynamics from a pressure waveform and relate it to volume. The main issue with current devices, is they can perform poorly during and after a significant hemodynamic event. An existing pulse contour analysis method, under ideal experimental conditions, demonstrated the ability to track changes in stroke volume (SV) using a measure of pulse wave velocity (PWV). In this study, the existing method’s ability to estimate SV was tested during vena cava occlusions (VCO), a worst case, rapid transient hemodynamic change. Additionally, the method’s sensitivity to the location of the arterial pressure waveform measurement was also assessed, by comparing SV estimates from aortic and iliac pressures, to SV measured by admittance catheter in the ventricle. Results show the model accurately tracks changes in SV as a result of the occlusion, a significant improvement over current commercially available devices. Bland-Altman analysis showed no significant improvement in SV estimation when using aortic pressure compared to the iliac pressure waveform, with mean bias of -2.11ml and 0.13ml, respectively. This is a desirable result, as more distal arterial pressure measurement locations increase the clinical feasibility of the method.

Use of the Kalman Filter for Aortic Pressure Waveform Noise Reduction.

Clinical applications that require extraction and interpretation of physiological signals or waveforms are susceptible to corruption by noise or artifacts. Real-time hemodynamic monitoring systems are important for clinicians to assess the hemodynamic stability of surgical or intensive care patients by interpreting hemodynamic parameters generated by an analysis of aortic blood pressure (ABP) waveform measurements. Since hemodynamic parameter estimation algorithms often detect events and features from measured ABP waveforms to generate hemodynamic parameters, noise and artifacts integrated into ABP waveforms can severely distort the interpretation of hemodynamic parameters by hemodynamic algorithms. In this article, we propose the use of the Kalman filter and the 4-element Windkessel model with static parameters, arterial compliance C, peripheral resistance R, aortic impedance r, and the inertia of blood L, to represent aortic circulation for generating accurate estimations of ABP waveforms through noise and artifact reduction. Results show the Kalman filter could very effectively eliminate noise and generate a good estimation from the noisy ABP waveform based on the past state history. The power spectrum of the measured ABP waveform and the synthesized ABP waveform shows two similar harmonic frequencies.

Model-based cardiovascular disease diagnosis: a preliminary in-silico study.

In this study, we developed and examined the feasibility of a model-based system identification approach to cardiovascular disease diagnosis. The basic premise of the approach is that it may be possible to diagnose cardiovascular disease from disease-induced alterations in the arterial mechanical properties manifested in the proximal and distal arterial blood pressure waveforms. It first individualizes the lumped-parameter model of wave propagation and reflection in the artery using the measurement of proximal and distal arterial blood pressure waveforms. Then, it employs a diagnosis logic, in the form of disease-specific patterns in model parameters, referred as [Formula: see text] and pulse transit time. The longitudinal change in these parameters is used to diagnose the presence of peripheral artery disease and arterial stiffening. We illustrated the feasibility of the proposed approach by testing it in a full-scale in-silico arterial tree simulation. The results showed that the approach exhibited superior sensitivity to ankle-brachial index and convenience to carotid-femoral pulse wave velocity: The model parameters [Formula: see text] and [Formula: see text] responded with up to 100 and 40% changes to peripheral artery disease with up to 50% arterial blockage whereas the change in ankle-brachial index was [Formula: see text]; the same parameters responded with up to 300 and 40% changes to up to 100% arterial stiffening while pulse transit time changed by up to 24%. Together with the development of more convenient techniques for the measurement of arterial blood pressure waveforms, the proposed approach may evolve into a viable alternative to the state-of-the-art techniques for cardiovascular disease diagnosis.